The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/660,424, filed 10 Mar. 2005.
The present invention relates to the precise manufacture of precision gear teeth and splines, and more particularly to a system and method to precisely hone heat treated gears and splines with a high hardness utilizing a gear shaper machine with Cubic Boron Nitride (CBN) tooling.
Machining is normally required on precision gear teeth after the heat treat process due to the distortion or warp induced on the workpiece by the heat associated with the heat treat process. Some distortion is an inherent and inevitable result of heat treatment. The distortion, however, is unacceptable on precision aerospace gears and splines when design tolerances are exceeded.
One method for machining precision gears in the hard state after the heat treat process is grinding with an abrasive wheel type media such as aluminum oxide or Cubic Boron Nitride (CBN) tooling. In many cases, however, it may not be possible to grind with a wheel type grinder due to part geometry limitations that may create an interference condition.
Lapping and honing methods have also been utilized but may have limited results because these machining methods may not provide the accuracy demanded in aerospace quality gears and splines. Typical lapping machines drive the workpiece at the headstock and the cutter tooling is then driven by the workpiece in an idler mode. This method tends to damage the involute form and may create an undesirable step condition in the root of the tooth. Lapping also cannot correct tooth to tooth spacing error, accumulated spacing error, lead error, involute error, concentricity error, or roundness errors. Typical computer numerically controlled honing machines are effectively utilized in some aerospace applications, but the machines may be cost prohibitive as such machines require vitrified type cutter tooling with diamond dressings.
Due to the limitations stated above, aerospace quality internal and external gears and splines are typically finish machined prior to the heat treat process with the expectation that the workpiece will not distort beyond desired design tolerances. Although effective, some percentage of the workpieces will distort beyond design tolerances and are scrapped due to the lack of an effective rework process.
Accordingly, it is desirable to provide a system and method to precisely machine aerospace quality gears and splines after a heat treat process which minimizes tooth to tooth spacing error, accumulated spacing error, lead error, involute error, concentricity error, roundness errors, pin size error or minor/major diameter errors to reduce scrap rates thereof.